This invention relates to the field of manufacture of semiconductors and other electronic devices wherein a substrate or wafer must be dried.
Prior methods and apparatus for drying semiconductor substrates or wafers involved introducing a drying alcohol such as isopropyl alcohol (IPA) into a process chamber in vapor form. For example, Kedo, et al, U.S. Pat. No. 6,219,936 discloses jetting liquid phase IPA at a temperature higher than that of the wafers in the vicinity of jetting openings where nitrogen gas is simultaneously introduced. The pure water held on the surfaces of the wafers is replaced in Kedo""s system by IPA in mist form, and then evaporated from the surface of the wafers to cause drying.
Mohindra, et al., U.S. Pat. No. 5,571,337, discloses bubbling nitrogen gas through IPA in a vessel, and then introducing the resultant gas containing a trace amount of IPA vapor into the process chamber.
McConnell, et al., U.S. Pat. No. 4,984,597, discloses a vaporizer with automatic refill mechanism to produce saturated drying vapor outside the chamber, which is then introduced into the process vessel and flashed to a superheated vapor.
Ferrell U.S. Pat. No. 5,685,086, discloses use of nozzles within the process vessel to generate aerosols.
There are several disadvantages to the prior art systems and methods wherein IPA vapor must be generated outside the process vessel or aerosols generated with nozzles within the process vessel.
It is an object of the present invention to provide a more efficient method and apparatus for generating drying alcohol vapor in connection with drying semiconductor wafers or substrates.
It is another object of the invention to avoid the separate components and process steps involved in generation of drying alcohol vapor required by the prior art systems.
Another object of the present invention is to provide a process and apparatus for a more through drying of, superior particle performance on, and increased throughput in, the processing of substrates which includes a Marangoni effect drying step.
These objects, and others which will become apparent from the following disclosure and drawings, are achieved by the present invention which comprises in one aspect a method of drying semiconductor wafers or substrates comprising introducing an polar organic compound in liquid form onto or into means for enhancing evaporation within a process chamber, causing the liquid to evaporate and form a drying vapor within the process chamber.
In another aspect, the invention comprises apparatus for drying semiconductor wafers or substrates comprising a process chamber, an evaporation enhancing material or device within the chamber, and a system to introduce polar organic compound in liquid form into or onto the evaporation enhancing material or device, whereby the polar organic compound is converted from liquid form to vapor form within the chamber.
Preferred polar organic compounds are the ones which are conventionally used in Marangoni effect drying of semiconductor wafers or substrates, for example alcohols such as isopropyl alcohol (IPA), 1-methoxy-2-propanol, and di-acetone alcohol. IPA is most preferred.
Suitable evaporation enhancing materials or devices for use within the process chamber include a porous tube, a filter element, or an open trough. Other materials or devices can also be used if they efficiently enhance evaporation and do not introduce any particles.
In the case of the porous tube, it is preferable to use a tube having micropores of about 20 to 50 microns in diameter. In the case of a trough, a suitable one is an open, flat bottomed trough made of a fluoropolymer such as polyvinylidene fluoride (PVDF).
Other suitable porous materials are those used in conventional filter elements, as long as they do not generate particles. In the case of the trough, a tube can be used for introducing the liquid polar organic compound into the trough, and a processor-controlled valve or series of valves can be used for controlling the rate of flow of polar organic compound into the trough.
In the case of a filter element or the porous tube, evaporation rate of the polar organic compound is increased by at least an order of magnitude by a wicking action by capillary effect that increases the surface area of the polar organic compound.
The filter element is preferably a fluoropolymer in a filter assembly positioned in an upper area of the process chamber, the element having a surface area of about 100 to 800 cm2 and being capable of being wetted with the polar organic compound. A preferred fluoropolymer for the filter element is polytetrafluorethylene (PTFE).
The flow control system can include a number of valves which are controlled by software and hardware, including a processor, so that the rate of flow of the alcohol into the chamber and onto the evaporation enhancing material or device can be precisely controlled, which in turn governs the evaporation rate. The flow control system preferably includes a pair of three-way valves separated by a length of tubing, a source of pressurized inert gas, a source of liquid polar organic compound, and a control system for switching the valves so that the gas pushes the liquid into the tank at a controlled rate.
The evaporation enhancing material or device, for example the filter element, porous tube, or open trough, is preferably positioned in an upper area of the chamber.
It is highly preferred that there is no generation of alcohol vapor outside the chamber, or jetting of liquid phase alcohol within the chamber, since avoidance of such systems is an objective of the invention. However, in some systems it may be suitable to introduce some of the alcohol by the prior methods involving ionization, vaporization, or jetting along with nitrogen.
The temperature and pressure within the chamber is preferably ambient, with temperature about 20 to 25xc2x0 C.
Ionization is preferred, and the ionization system preferably includes an ionizer which is controlled by a processor so as to activate ionization when the polar organic compound is being evaporated within the process chamber and thereby converted to vapor. The ionization is preferably supplied by nitrogen gas from a separate supply tube and manifold within the process tank or other than that of the drying vapor generation system supply tube. A preferred ionizer comprises a nuclear anti-static device using a Polonium-210 radioisotope which emits alpha particles which produce millions of ion pairs that in turn drain electrostatic charges off liquid surface particles and substrates during a period when the Marangoni effect is in progress within the process tank.
The preferred system for controlling the introduction of liquid polar organic solvent contains two three-way valves separated by a length of tubing, a source of pressurized inert gas, a source of liquid polar organic compound, and a control system for switching the valves so that the gas pushes the liquid into the tank at a controlled rate.